The present invention relates to a wet-type exhaust gas desulfurizing apparatus for a thermal power station or the like, and more particularly to a wet-type exhaust gas desulfurizing apparatus suitable for accelerating oxidation of sulfurous calcium produced in absorber slurry.
A desulfurizing apparatus according to a limestone-plaster method is well known as a wet-type exhaust gas desulfurizing apparatus, which is used for absorbing sulfur oxide (hereinafter abridged as SOx) contained in the exhaust gas while using a calcium compound as an absorber, and for softening sulfurous calcium produced through the reaction into plaster that is stable. The plaster is collected by an auxiliary produced material.
The desulfurizing reaction according to the limestone plaster is represented by the following formulae. EQU CaCO.sub.3 +SO.sub.2 +1/2H.sub.2 O.fwdarw.CaSO.sub.3.1/2H.sub.2 O+CO.sub. EQU CaSO.sub.3.1/2H.sub.2 O+1/2O.sub.2 +3/2 l H.sub.2 O.fwdarw.CaSO.sub.4.2H.sub.2 O
In such a conventional wet-type exhaust gas desulfurizing apparatus, an absorbent tower for absorbing SOx contained in the exhaust gas by contacting the slurry containing the absorber with the exhaust gas in a gas-liquid phase and an oxidizing tower for oxidizing sulfurous calcium that is formed through the reaction are provided separately from each other.
In order to simplify the structure of this apparatus, the present applicants have proposed, as in Japanese Utility Model Unexamined Publication No. 60-132830, another apparatus in which the absorbing reaction and the oxidation reaction are carried out in a single tower. Namely, in that apparatus, air is blown to a portion close to an agitator provided within a slurry recirculation tank located in a lower portion of the absorbing tower, so that the sulfurous calcium contained in the slurry is oxidized with the air bubbled by the agitator.
FIG. 18 shows an overall schematic view of that apparatus. The latter is composed mainly of a dust removing tower 102 for removing dust from an exhaust gas 101 and an absorbing tower 103 for absorbing SOx contained in the exhaust gas 101, oxidizing the chemical products produced through the desulfurizing reaction and collecting the products as plaster.
The exhaust gas 101 supplied from a boiler (not shown) is processed through dust-removal and is cooled in the dust removing tower 102, if necessary. In the dust removing tower 102, a recirculation fluid 105 contained in a recirculation tank 104 is raised by a recirculation pump 106. The recirculation fluid 105 is sprayed within the dust removing tower 102 for removing dust, hydrogen chloride (HCl) and hydrogen fluorine (HF) from the exhaust gas. Agitators 107 for preventing precipitation are provided within the recirculation tank 104.
The exhaust gas 101 from which the dust has been removed is fed to the absorbing tower 103 where the exhaust gas is brought into contact with absorbent slurry 109 composed mainly of limestone and plaster and sprayed from spraying portions 108. The exhaust gas 101 from which SOx is removed through the contact is passed through a demister 110 and then is discharged from a top portion of the absorbent tower 103 to the outside.
The slurry 109 that has absorbed SOx falls downwardly and is temporarily retained in a slurry recirculation tank 111 provided integrally with a lower portion of the absorbent tower 103. The retained slurry 109 is agitated by agitators 112A provided in the lower portion of the tank 111 and is fed to the spraying portions 108 of the upper portion of the absorbent tower 103 through a slurry line 114 by a recirculation pump 113. The above-described absorbing operation is repeated.
On the other hand, air pressurized by a compressor 115 is supplied to a portion close to agitators 112B for the oxidation reaction through air feed pipes 117. The air is bubbled by the agitation action of the agitators 112B to oxidize sulfurous calcium in contact with the slurry 109 retained in the tank 111.
In this apparatus, it should be, however, noted that the air 116 is supplied through only one portion relative to a rotary vane of each oxidation agitator 112B. In addition, due to the fact that a specific weight of the air 116 is much smaller than that of the slurry 109, the region close to the rotary vane is separated into a region where a large amount of air is present and another region where a large amount of slurry 109 is present. As a result, the air 116 will not be sufficiently bubbled into fine bubbles in the slurry 109. Also, the air is brought into contact with the slurry 109 under the condition that the bubble size of the air be kept at a relatively large level, so that the oxidation of the sulfurous calcium would not be well performed as a whole.
Also, as described above, the two portions which are composed mainly of air 116 and slurry 109, respectively, are formed in the rotary region of the vane, so that an unbalanced load is imposed on the agitator 112B. As a result, the apparatus would suffer a technical problem such as generation of vibration and noises.
FIGS. 19 and 20 are a partially sectional front view and a partially sectional plan view showing a soda water producing apparatus disclosed in U.S. Pat. No. 2,404,679.
Referring to FIGS. 19 and 20, water 151 is held in a tank 150, bearings 154a and 154b are mounted on central portions of an upper cover 153 and a bottom plate 152, respectively. A hollow rotary shaft 155 is rotatably supported between the upper and lower bearings 154a and 154b. Spinning tubes 156 and rotary vanes 157 are alternately provided in plural stages around and on a portion of the rotary shaft 155 dipped into the water 151.
In the upper cover 153, there is formed a pressure gas feed path 158 whose tip end is in communication with an axial hole 159 of the rotary shaft 155. The lower end of the axial hole in turn is closed as shown in FIG. 20.
A carbonated gas 160 fed under pressure from the pressure gas feed path 158 is passed through the axial hole 159 and is injected into the water from the respective spinning tubes 156 as bubbles 161. The injection energy of the carbonated gas 160 injected from the spinning tubes 156 causes the spinning tubes 156 and the rotary vanes 157 to rotate together in the clockwise direction as shown in FIG. 20. As a result, the water 151 is agitated within the tank 151.
However, in this apparatus, since the spinning tubes 156 and the vanes 157 are rotated together, there is almost no relative movement between the bubbles 161 and the vanes 157. As a result, relatively large bubbles are generated unlike the present invention according to which minute bubbles are generated due to shearing effect concomitant with the rotation of the vanes 157 as later described. Also, if the feed pressure of the carbonated gas 160 would be increased in order to sufficiently effect the agitation of the rotary vanes 157, the bubbles 161 would be injected radially outwardly beyond the rotary region 162 of the vanes 157 (see FIG. 20) so that there would be almost no contact with the rotary vanes 157. In this case, a desired agitation or mixture would not be attained.